* YAM_WR.c: changed the mail composition to use the original file's name in
the Content-Disposition header instead of the current file name. This fixes
the problem, that attachments are shown with wrong name on other systems if
one attaches a file to mail, puts the mail on hold, edits it later and
finally sends it off. In this case YAM changed the original file name to the
one used internally by YAM (YAMm00000123.txt for example).

* YAM_CO.c, YAM_FI.c: comparing an empty list against a non-empty list falsely
signaled both lists to be equal. This effectively prevented saving the
conifiguration when i.e. starting with an empty MIME type list and adding
new entries without changing anything else in the configuration.

* mui/MainMailList.c: the context menu's "Set status to" entries are now
enabled/disabled in respect to the number of selected mails. For a single
mail the menu items reflect the current state of the mail and opposite items
will be disabled. For multiple mails opposite items will both be enabled
(i.e. "read" and "unread") to give the user the chance to modify the status
independent of the clicked mail. This fixes bug #2177452.